1. Field of the Invention
The present invention relates generally to the field of golf club head manufacture and more specifically to an improved investment or lost wax casting process and to a collapsible insert that may be used in that process to fabricate a golf club head iron or putter having a peripherally weighted rear cavity with an undercut region along the radial periphery of the cavity.
2. Prior Art
It is well-known in the golf club head art to use an investment lost wax casting process to manufacture such golf club heads. In this process, a wax duplicate of the desired golf club head configuration is first manufactured using a mold tool into which hot wax is injected. The mold tool provides an injection cavity which is shaped precisely congruent to the desired configuration of the golf club iron or putter head. When the wax cools and the molding tool is opened, the wax casting is removed and may be then used as an investment casting, whereby molten metal, such as steel having chemistries normally used in the fabrication of golf club heads, may be poured into a ceramic casing formed around the wax casting which is melted and burned out of the hot ceramic slurry. The metal forms in the casing into the exact same shape as the melted wax casting. Thus, it can be seen that the wax casting must be precisely the same shape and configuration as the desired shape of the ultimate product, namely the metal version of the golf club head iron or putter.
In the manufacture of modern golf club iron heads, it has been recognized that improved performance of the golf club head can be achieved by providing a peripheral weight distribution to minimize the negative impact of off-center hits on the golf ball. To achieve such peripheral weight distribution it has become common to provide a rear cavity surrounded by a peripheral mass. The desire to distribute the peripheral weight as far as possible from the center of gravity of the golf club iron head has resulted in still a further change in the configuration of the golf club head, namely, the use of an undercut region between the peripheral mass and the rear wall of the hitting surface that defines the forward most surface of the rear cavity.
While such an undercut region may improve the performance of the golf club head, it has the disadvantage of increasing the difficulty of fabricating the wax casting because the wax version of the golf club head must also have the rear cavity undercut region in order to result in a head that has that undercut region. It is therefore well-known in the prior art to use a special insert in the wax casting mold tool to define and maintain an undercut region while the molten wax is injected into the tool. A difficulty in the fabrication process comes from the need to remove the insert from the wax casting after the wax has been cooled and without damaging the surface of the wax casting which would otherwise negatively impact the aesthetic appearance of the resulting iron head.
One such prior art insert comprises a plurality of undercut insert portions typically made of a metal or ceramic material and which can be readily positioned in the mold tool before the wax is injected. The multi-piece insert then comes out with the wax investment casting and can be readily removed after the wax has cooled by simply removing one piece at a time. If enough pieces are used depending on the extent of the undercut, the removal of the insert pieces can usually be accomplished without disturbing the surface of the wax. Unfortunately, as will be seen hereinafter in more detail, a multi-piece insert requires that the various pieces abutt one another, thus forming butt lines. No matter how perfectly matched the individual pieces are at their respective ends, the butt lines are unavoidable and the butt lines produce corresponding butt line impressions in the wax adjacent the insert, along the peripheral portion of the rear cavity. Such line impressions (flash) thus appear in the wax casting and ultimately appear in the metal head which can detract from the aesthetic appearance of the head. Furthermore, they can result in ceramic inclusion and difficult secondary finishing which is expensive and time-consuming. Consequently, there is a substantial disadvantage to using a multi-piece insert to produce an undercut region along the rear cavity periphery of a wax casting.
Another prior art alternative is to use a single piece insert, but made out of a material which can be readily broken apart and also removed piece by piece from the cooled metal head. By way of example, in the prior art a typical single piece insert for this purpose may be made out of a brittle material, such as a readily breakable ceramic which can be broken out of the cast metal head after it has cooled. Unfortunately, such a brittle insert is expensive and can add considerably to the overall cost of the manufacture of the head. Because each such insert is broken away from the finished head, it can only be used once and thus every head requires the investment of one brittle insert, a very expensive procedure. Furthermore, there is the possibility that the brittle inserts will not be consistent in size.
Still another prior art insert technique for generating undercut regions in golf club heads, involves the use of soluable wax which must be dissolved using a solution such as citric acid solution which also adds to the time and expense of fabrication.
The applicant herein has conducted a novelty search of the prior art, the results of which are as follows:
U.S. Pat. No. 4,929,403 to Audsley is directed to the composition of and the process for forming flexible molds used in casting finely detailed objects. While the reference focuses on the radiatively curing procedure and the elaborate combination of materials that go into the fabricating process, the end result is an elastic, flexible mold for use in casting reproductions of the finely detailed object that will ultimately be produced. Among the various reproduction types to be cast from the mold is a wax reproduction for use in the lost wax process.
U.S. Pat. No. 4,682,643 to Bernhardt et al is directed to an investment casting process which in one embodiment employs a reusable, resilient pattern to form molds having a multi-cavity structure. In that embodiment, the pattern is formed by curing in the desired shape a quantity of flowable silastic rubber. Molds may then be shaped by casting around this pattern a quantity of various mold materials. After the mold so shaped has cured, the deformable rubber pattern is mechanically removed for reuse in forming another mold.
U.S. Pat. No. 4,027,723 to Maurino et al is directed to an apparatus for producing female molds for use in the casting of brake drums. As shown in FIGS. 3 and 4, the inner cavity of the female mold 26 is formed by use of a flexible male mold 1 having a plurality of projections 5 extending radially outward to form corresponding projections in the female mold 26 that extend radially inward. The elastomeric properties of the male mold 1 facilitate the formation of such projections on the female mold 26 by allowing the male mold 1 to collapse radially inward when a vacuum is drawn around it. The collapse of the mold 1 causes its projections 5 to be withdrawn from the corresponding cavities (between the projections created) formed in the female mold 26 so that the male mold 1 may be removed from the female mold cavity without damage to the radial projections formed therein.
U.S. Pat. No. 4,378,044 to Suchan is directed to a pattern for use in casting molds of cast pieces having at least one undercut. As the undercut is intended to be formed here by the application of pressure during final compacting of the mold material, pattern 1 (FIG. 1), comprises a rigid portion 2 and a deformable rubber top portion 3. The rubber top portion 3 is shaped such that, under stress, it deforms into the shape outlined by the broken line 5 to form a bulge 6 for creating the undercut in the mold being cast. The inventor here states that the unstressed shape of the rubber top portion 3 and the hardness of the rubber forming that portion may be varied to obtain desired casting results.
U.S. Pat. No. 4,472,092 to Schmidt is directed to the fabrication of a golf club head having a metallic shell construction. The process here does not necessarily employ a reusable core for casting a mold; however, the process does incorporate the lost wax procedure to ultimately form a metallic golf club head having an internal cavity. Although the process calls for the core 10 of FIG. 1 to be chemically dissolved after the wax shell 15 is formed, the inventors state that various materials including styrofoam and other synthetic resins may be employed for the core.
Other patent references, namely, U.S. Pat. No. 3,396,934 to Ferris; U.S. Pat. No. 4,499,940 to Hall; U.S. Pat. No. 5,066,213 to Ferincz; U.S. Pat. No. 5,247,984 to Stanciu; and U.S. Pat. No. RE 34,862 to Czor are all directed to other systems of even less relevance to the present invention.
Unfortunately, none of the aforementioned prior art patents discloses any means for overcoming the disadvantages of the previously described prior art and thus there remains a need for providing an improved investment wax casting process for golf club heads having an undercut region adjacent the rear cavity peripheral mass of the golf club head.